"But the messages that Kronecker did communicate contained some very important truth; in particular he complained that much of set theory was fantasy because it was not algorithmic (that is, it contained no rule by which one could decide, in a nite number of operations, whether a given element did or did not belong to a given set). Today, with our computer mentalities, this seems such an obvious platitude that it is hard to imagine anyone ignoring it, much less denyingit; yet that is just what happened. We think that, had mathematicians paid more attention to this warning of Kronecker, mathematics might be in a more healthy state today."